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용접부 균열의 크리프-피로 균열성장 수명평가 연구 (Ⅱ)
윤기봉(Kee Bong Yoon),백운봉(Un Bong Baek),이해무(Hae Moo Lee),서창민(Chang Min Suh) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of 1Cr-0.5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the C-parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of (da/dt)<SUB>avg</SUB> vs. (C<SUB>t</SUB>)<SUB>avg</SUB> for residual life assessment.
윤기봉(K.B.Yoon),마영화(Y.W.Ma),김영일(Y.I.Kim),차석주(S.J.Cha),김윤재(Y.J.Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
In this paper the causes and mechanisms of the failure of gas turbine compressor blades were analyzed with finite element analysis and surface inspection. An approximate remaining life assessment was performed by deterministic assessment methods based on the results of fatigue crack growth tests and collected mechanical properties data
윤기봉(Kee Bong Yoon),응웬반장(Nguyen Van Giang),위엔두안선(Nguyen Tuan Son),정성용(Seong Yong Jeong),이주영(Joo Young Lee),김지윤(Ji Yoon Kim) 한국가스학회 2013 한국가스학회지 Vol.17 No.2
공정플랜트에는 다양한 배관이 고압, 고온의 인화성, 폭발성 물질을 이송하고 있다. 잦은 설계 변경 및 증설 등으로 복잡한 형상으로 배관이 형성되어 있는 경우가 많으나 배관의 구조가 단순하여 실제 위험성에 비해 안전 관리가 부족한 경우가 많다. 본 연구에서는 국내 한 업체에서 부생가스를 연료로 사용하던 배관을 설계 변경하여 천연가스와 혼합하여 사용하도록 사례를 활용하여, 배관의 안전성을 평가 하는 방법을 예시하였다. 배관의 설계 변경 후 안전성을 ASME 기준에 따라 재평가하고, 배관의 주요 관리부위를 결정하는 방법을 제시하였다. 배관의 분기 및 루프 등이 다수 복잡하게 연결되어있는 가스혼합용 믹싱드럼 배관 시스템을 대상으로 해석하였다. 배관의 주요부위 응력 민감도를 이해하기 위해 배관의 지지대 구속조건 및 외부 온도를 변화시켜 가면서 이들의 영향을 연구하였다. 또한 부생가스가 포함하고 있는 수소가스에 의한 손상 가능성에 대해서도 논의하였다. Various process piping usually carries out high flammable and explosible gas under high pressure and high temperature. Due to frequent change of design and structure it becomes more complicated and compactly located. The safety management level is relatively low since it is considered as simply designed component. In this study a safety assessment procedure is proposed for complicated piping system around a mixing drum in which natural gas and by-product gases were mixed. According to ASME code, pipe stress analysis was conducted for determining design margin at some key locations of the piping. These high stress locations can be used as major inspection points for managing the pipe integrity. Sensitivity analysis with outside temperature of the pipe and support constraint condition. Possible effect of hydroen gas to the pipe steel during the previous use of the by-product gas was also discussed.
감육배관의 저주기 피로 평가를 위한 국부 탄소성 변형률 평가 방법
윤기봉(Kee Bong Yoon),마영화(Young Wha Ma),안중혁(Joong Hyok An),김윤재(Yun Jae Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In order to assess the integrity of pipes with local thinning area, the plastic strain as well as the elastic strain at the root of thinned region are required particularly when fluctuating load is applied to the pipe. For estimating elastic-plastic strain at local wall thinning area in a straight pipe under tensile load, an estimation model with idealized fully circumferential constant depth wall thinning area is proposed. Based on the compatibility and equilibrium equations a nonlinear estimation equation, from which local elastic-plastic strain can be determined as a function of pipe/defect geometry, material and the applied strain was derived. Estimation results are compared with those from detailed elastic-plastic finite element analysis, which shows good agreements. Noting that practical wall thinning in nuclear piping has not only a circular shape but also a finite circumferential length, the proposed solution for the ideal geometry is extended based on two-dimensional and three-dimensional numerical analysis of pipes with circular wall thinning.